Stainless Steel Coil Tube (Coiltube) for HVAC Fan Coil Unit Systems
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled piping product specifically designed for use in Fan Coil Unit (FCU) plus Fresh Air Air Conditioning Systems. This product serves as a critical heat exchange and fluid distribution component within commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) infrastructure. The coil tube is formed into continuous helical or spiral configurations to maximize surface area within constrained installation spaces, enabling efficient thermal transfer in chiller loops, hydronic heating circuits, and ventilation duct integration systems.
As a key structural element in modern building climate control, this coil tube product meets the rigorous demands of variable air volume (VAV) systems, constant volume systems, and hybrid fresh air introduction architectures. The product is catalogued under reference number 1235 and classified within the technical literature and engineering design documentation framework.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional corrosion resistance, mechanical durability, and thermal conductivity properties essential for HVAC applications.
Material Composition
- Primary Grades: SUS304 (ASTM A269 TP304), SUS316 (ASTM A269 TP316), SUS321 (ASTM A269 TP321)
- Chromium (Cr): 18–20% (SUS304); 16–18% (SUS316)
- Nickel (Ni): 8–10% (SUS304); 10–14% (SUS316)
- Molybdenum (Mo): 2–3% (SUS316, for enhanced chloride resistance)
- Carbon (C): ≤0.08% (SUS304); ≤0.03% (SUS304L, low-carbon variant)
Key Mechanical & Physical Properties
- Tensile Strength: ≥520 MPa (SUS304); ≥515 MPa (SUS316)
- Yield Strength: ≥205 MPa
- Elongation: ≥40% (at fracture)
- Thermal Conductivity: 14.9 W/(m·K) (SUS304 at 20°C); 16.3 W/(m·K) (SUS316 at 20°C)
- Operating Temperature Range: −196°C to +870°C (SUS304); −196°C to +925°C (SUS316)
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, chlorides, and deicing chemicals
- Sanitary Performance: Hygienic, non-toxic, non-tarnishing surface suitable for potable water and food-grade HVAC systems
Specifications
| Parameter | Specification |
|---|---|
| Product Reference No. | 1235 |
| Product Category | Coil Tube (Coiltube) — Literature/Engineering Design Reference |
| Outer Diameter (OD) | 6.35 mm, 9.53 mm, 12.70 mm, 15.88 mm, 19.05 mm (1/4" to 3/4" nominal) |
| Wall Thickness | 0.50 mm – 1.50 mm (customizable per application requirements) |
| Coil Pitch (Spacing) | 8 mm – 25 mm (adjustable based on heat exchange efficiency needs) |
| Coil Diameter | 300 mm – 1200 mm (configurable for FCU housing dimensions) |
| Coil Turns | 4 – 16 passes (dependent on thermal load requirements) |
| Surface Finish | Ba < 0.4 μm (electropolished); Ra ≤ 0.8 μm (standard polished) |
| End Connection Type | Flared, threaded (BSP/NPT), socket-weld, or brazed |
| Pressure Rating | Up to 1.6 MPa (standard); up to 4.0 MPa (heavy-wall variant) |
| Flow Capacity | 0.5 – 12.0 L/min (per pass, depending on diameter and pressure) |
| Applicable Standards | ASTM A269, ASTM A213, EN 10216-5, GB/T 12771, JIS G3459 |
| Maximum Coil Length | Up to 50 meters per continuous coil assembly |
| Finish Options | Mirror polished, satin, matte, or passivated |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical integrity, and long-term service reliability in HVAC environments.
Process Flow
- Raw Material Selection & Inspection: Stainless steel seamless or welded tube stock (conforming to ASTM A269 or EN 10216-5) is procured from certified mills. Incoming material undergoes spectroscopic composition analysis (OES), hardness testing, and visual inspection for surface defects.
- Cut & Deburring: Tubes are precision-cut to specified lengths using CNC plasma or laser cutting systems. Edges are deburred and chamfered to prevent flow turbulence and ensure clean coil formation.
- Coil Forming (Rolling): The straight tube is fed through a multi-roller forming station where progressive die rolls gradually bend the tube into the desired helical geometry. The forming process is performed at ambient temperature (cold-forming) to preserve material properties and avoid work-hardening issues. Roller configurations are adjusted to achieve the specified coil diameter, pitch, and number of passes.
- Stress Relief Annealing: Following coil formation, the product undergoes controlled heat treatment (annealing) at 850°C – 1050°C in a protective atmosphere (argon or nitrogen) to relieve residual stresses introduced during cold forming. This step restores full ductility and prevents stress-corrosion cracking (SCC) susceptibility.
- Pickling & Passivation: The annealed coil tube is subjected to acid pickling (mixed HNO₃/HF or citric acid bath) to remove oxide scale. A subsequent passivation treatment (nitric acid or citric acid immersion) establishes a stable chromium oxide passive film, enhancing corrosion resistance.
- Surface Finishing: Depending on the application, the coil tube receives electropolishing (for Ba < 0.4 μm finish), mechanical polishing, or brushing to achieve the specified surface roughness. This is critical for minimizing fouling and maintaining efficient heat transfer in hydronic systems.
- End Fitting & Assembly: Coil ends are fitted with flared, threaded, or flanged connections as specified. Brazing (using silver-based filler alloy) or orbital TIG welding (GTAW) is performed for leak-tight joints.
- Pressure & Leak Testing: Each coil tube assembly undergoes hydrostatic pressure testing at 1.5× the maximum operating pressure for a minimum of 30 minutes. Helium leak detection (for critical applications) may be employed to verify joint integrity at sensitivities of 1×10⁻⁹ Pa·m³/s.
- Final Quality Inspection & Packaging: Dimensional verification (OD, wall thickness, coil diameter, pitch) is performed using calibrated gauges and CMM (Coordinate Measuring Machine). The product is packaged in protective crates with desiccant to prevent atmospheric corrosion during transit.
Applications
The stainless steel coil tube is integral to the design and operation of Fan Coil Unit (FCU) plus Fresh Air Air Conditioning Systems, as documented in the engineering literature on HVAC design methodology. Primary application domains include:
Primary Applications
- Fan Coil Units (FCU): The coil tube serves as the heat exchange element within FCU casings, transferring thermal energy between the circulating hydronic fluid (hot water or chilled water) and the airstream drawn through the unit. The coil tube configuration directly determines the cooling/heating capacity (measured in BTU/hr or kW) of the FCU.
- Fresh Air Handling Units (FAHU): In combined FCU + Fresh Air systems, coil tubes are used in the pre-conditioning section of fresh air handlers to temper incoming outdoor air before mixing with recirculated air, improving overall system efficiency and indoor air quality (IAQ).
- Commercial Building HVAC: Office buildings, hotels, hospitals, and retail spaces utilize these coil tubes in per-zone temperature control architectures where individual room units provide precise climate management.
- Industrial Process Cooling: Precision coil tubes are deployed in cleanroom HVAC systems, semiconductor fabrication facilities, and pharmaceutical manufacturing environments where ultra-low particulate and chemical-free air supply is mandated.
- Residential HVAC Systems: High-end residential applications featuring zoned climate control with in-duct or ceiling-mounted FCUs.
- Refrigeration & Chiller Circuits: Coil tubes in secondary loop piping for distributed refrigeration systems, including district cooling networks.
- Hydronic Radiant Systems: PEX-compatible stainless steel coil tubing for radiant floor and wall heating systems in commercial and institutional buildings.
System Design Context
In the design methodology for FCU + Fresh Air Air Conditioning Systems, the coil tube selection is governed by several critical parameters: the design cooling/heating load (calculated per zone based on heat gain analysis), the supply air temperature differential (typically ΔT = 10–14°C for cooling), the water-side flow rate and temperature (chilled water: 7°C supply / 12°C return; hot water: 45°C supply / 40°C return), and the air-side velocity (maintained below 2.5 m/s to limit noise and ensure even distribution). The coil tube geometry—specifically the number of passes, tube diameter, and pitch—must be optimized to achieve the target heat transfer coefficient (U-value typically 25–40 W/m²·K for air-to-water coil tubes) while minimizing pressure drop on both the air and water sides.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and certifications to assure product conformity with international standards:
Certifications
- ISO 9001:2015 — Quality Management Systems (QMS)
- ISO 14001:2015 — Environmental Management Systems (EMS)
- ISO 45001:2018 — Occupational Health and Safety Management Systems
- CE Marking — European Conformity (compliance with EU Pressure Equipment Directive PED 2014/68/EU where applicable)
- NSF/ANSI 61 — Drinking Water System Components (for potable water contact applications)
- 3-A Sanitary Standards — Where applicable for food and beverage processing HVAC
- GB/T 19001 — Chinese National Quality Management Standard
Testing & Verification
- Chemical composition verification via Optical Emission Spectroscopy (OES)
- Mechanical property testing per ASTM A370 (tensile, yield, elongation)
- Hydrostatic pressure testing per ASTM A269 (1.5× working pressure, 30-minute hold)
- Corrosion testing: Salt spray (ASTM B117, 480-hour minimum), Ferric sulfate (ASTM A967)
- Dimensional inspection per ASTM A213/A269 tolerance tables
- Surface finish verification via profilometry (Ra, Rz measurement)
- Weld joint radiographic testing (RT) or ultrasonic testing (UT) for critical joints
Unique Selling Points
- Optimized for FCU + Fresh Air System Integration: Coil tube geometries are engineered specifically based on validated HVAC design methodologies, ensuring that thermal performance parameters (U-value, LMTD, effectiveness-NTU) are matched to the operating conditions of combined fan coil and fresh air architectures.
- Precision Coil Forming Technology: Proprietary multi-roller forming equipment ensures uniform coil pitch and diameter tolerances of ±0.5 mm, critical for consistent heat transfer and minimal pressure drop across the coil assembly.
- Superior Corrosion & Hygiene Performance: The use of SUS316 grade with molybdenum addition provides exceptional resistance to deicing salts and chlorinated cleaning agents commonly encountered in HVAC maintenance, extending service life beyond 25 years under normal operating conditions.
- Full Traceability: Each coil tube batch is traceable to the original mill certificate (Mill Test Report / MTR), with complete documentation of chemical composition, heat treatment, and test results available upon request.
- Customizable Configurations: Flexible manufacturing capabilities allow for custom coil diameters, pitches, pass counts, and end connection types to match specific OEM FCU designs and system-level engineering requirements.
- Low Fouling Factor: Electropolished surface finish (Ba < 0.4 μm) significantly reduces fouling accumulation on the water side, maintaining heat transfer efficiency over extended operating cycles and reducing maintenance intervals.
Technical Literature Reference
This product specification is informed by and aligned with the engineering design methodology described in "Design Methods for Fan Coil Unit Plus Fresh Air Air Conditioning Systems" (《风机盘管加新风空调系统的设计方法》), which provides the theoretical and practical framework for integrating coil tube components into high-performance, energy-efficient building climate control systems. The coil tube parameters specified herein are consistent with the thermal performance targets, airflow management strategies, and energy efficiency benchmarks established in this design literature.